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Avalanche Forecast

Archived

Nov 19th, 2020–Nov 20th, 2020

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Glacier.

This active weather pattern we are in has made for an active avalanche cycle in Glacier National Park. Consider overhead hazard traveling at lower elevations.

Weather Forecast

Today: Snow is forecasted to taper off to flurries, maybe 5 cm of accumulation, FL Hovering around HWY elevation, and mod SW winds

Tonight: Flurries, FL lowering to 700m, Moderate SW wind

Friday: 11cm of new snow, FL 1100m, Strong SW wind

Weekend: Cloudy with sunny periods

Snowpack Summary

40-90cm of Storm snow now covers the Nov 5th Crust, which exists up to 2500m on all aspects and higher on steep solar aspects. Reactive storm slabs have been observed in the upper snowpack at Alpine elev, and exposed areas of Treeline. Facets have also been observed on the Nov 5th crust, making for a excellent weak layer/bed surface combo.

Avalanche Summary

A modest natural avalanche cycle started yesterday morning, and is continuing today. Approx a dozen avalanches were obs in the HWY corridor in steep, unsupported terrain. Min reports from the Pterodactyl , Connaught drainage, and dispatches bowl of natural, and skier triggered avalanches. Storm and persistent slabs released to size 3.

Confidence

Timing, track, or intensity of incoming weather system is uncertain

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.